Abstract : This paper proposes Structured Data Nets (SDN), a Petri net extension that describes transactional systems with data. In these nets, tokens are semi-structured documents. Each transition is attached to a query, guarded by patterns, (logical assertions on the contents of its preset) and transforms tokens. We define SDNs and their semantics. We then consider their formal properties: coverability of a marking, termination and soundness of transactions. Unrestricted SDNs are Turing complete , so these properties are undecidable. We thus use an order on documents , and show that under reasonable restrictions on documents and on the expressiveness of patterns and queries, SDNs are well-structured transition systems, for which coverability, termination and soundness are decidable.